diff --git a/include/osmocom/sgsn/gprs_llc.h b/include/osmocom/sgsn/gprs_llc.h
new file mode 100644
index 0000000..376ae9a
--- /dev/null
+++ b/include/osmocom/sgsn/gprs_llc.h
@@ -0,0 +1,284 @@
+#ifndef _GPRS_LLC_H
+#define _GPRS_LLC_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <osmocom/sgsn/gprs_sgsn.h>
+#include <osmocom/sgsn/gprs_llc_xid.h>
+
+/* Section 4.7 LLC Layer Structure */
+enum gprs_llc_sapi {
+	GPRS_SAPI_GMM		= 1,
+	GPRS_SAPI_TOM2		= 2,
+	GPRS_SAPI_SNDCP3	= 3,
+	GPRS_SAPI_SNDCP5	= 5,
+	GPRS_SAPI_SMS		= 7,
+	GPRS_SAPI_TOM8		= 8,
+	GPRS_SAPI_SNDCP9	= 9,
+	GPRS_SAPI_SNDCP11	= 11,
+};
+
+/* Section 6.4 Commands and Responses */
+enum gprs_llc_u_cmd {
+	GPRS_LLC_U_DM_RESP		= 0x01,
+	GPRS_LLC_U_DISC_CMD		= 0x04,
+	GPRS_LLC_U_UA_RESP		= 0x06,
+	GPRS_LLC_U_SABM_CMD		= 0x07,
+	GPRS_LLC_U_FRMR_RESP		= 0x08,
+	GPRS_LLC_U_XID			= 0x0b,
+	GPRS_LLC_U_NULL_CMD		= 0x00,
+};
+
+/* Section 6.4.1.6 / Table 6 */
+enum gprs_llc_xid_type {
+	GPRS_LLC_XID_T_VERSION		= 0,
+	GPRS_LLC_XID_T_IOV_UI		= 1,
+	GPRS_LLC_XID_T_IOV_I		= 2,
+	GPRS_LLC_XID_T_T200		= 3,
+	GPRS_LLC_XID_T_N200		= 4,
+	GPRS_LLC_XID_T_N201_U		= 5,
+	GPRS_LLC_XID_T_N201_I		= 6,
+	GPRS_LLC_XID_T_mD		= 7,
+	GPRS_LLC_XID_T_mU		= 8,
+	GPRS_LLC_XID_T_kD		= 9,
+	GPRS_LLC_XID_T_kU		= 10,
+	GPRS_LLC_XID_T_L3_PAR		= 11,
+	GPRS_LLC_XID_T_RESET		= 12,
+};
+
+extern const struct value_string gprs_llc_xid_type_names[];
+
+/* TS 04.64 Section 7.1.2 Table 7: LLC layer primitives (GMM/SNDCP/SMS/TOM) */
+/* TS 04.65 Section 5.1.2 Table 2: Service primitives used by SNDCP */
+enum gprs_llc_primitive {
+	/* GMM <-> LLME */
+	LLGMM_ASSIGN_REQ,	/* GMM tells us new TLLI: TLLI old, TLLI new, Kc, CiphAlg */
+	LLGMM_RESET_REQ,	/* GMM tells us to perform XID negotiation: TLLI */
+	LLGMM_RESET_CNF,	/* LLC informs GMM that XID has completed: TLLI */
+	LLGMM_SUSPEND_REQ,	/* GMM tells us MS has suspended: TLLI, Page */
+	LLGMM_RESUME_REQ,	/* GMM tells us MS has resumed: TLLI */
+	LLGMM_PAGE_IND,		/* LLC asks GMM to page MS: TLLI */
+	LLGMM_IOV_REQ,		/* GMM tells us to perform XID: TLLI */
+	LLGMM_STATUS_IND,	/* LLC informs GMM about error: TLLI, Cause */
+	/* LLE <-> (GMM/SNDCP/SMS/TOM) */
+	LL_RESET_IND,		/* TLLI */
+	LL_ESTABLISH_REQ,	/* TLLI, XID Req */
+	LL_ESTABLISH_IND,	/* TLLI, XID Req, N201-I, N201-U */
+	LL_ESTABLISH_RESP,	/* TLLI, XID Negotiated */
+	LL_ESTABLISH_CONF,	/* TLLI, XID Neg, N201-i, N201-U */
+	LL_RELEASE_REQ,		/* TLLI, Local */
+	LL_RELEASE_IND,		/* TLLI, Cause */
+	LL_RELEASE_CONF,	/* TLLI */
+	LL_XID_REQ,		/* TLLI, XID Requested */
+	LL_XID_IND,		/* TLLI, XID Req, N201-I, N201-U */
+	LL_XID_RESP,		/* TLLI, XID Negotiated */
+	LL_XID_CONF,		/* TLLI, XID Neg, N201-I, N201-U */
+	LL_DATA_REQ,		/* TLLI, SN-PDU, Ref, QoS, Radio Prio, Ciph */
+	LL_DATA_IND,		/* TLLI, SN-PDU */
+	LL_DATA_CONF,		/* TLLI, Ref */
+	LL_UNITDATA_REQ,	/* TLLI, SN-PDU, Ref, QoS, Radio Prio, Ciph */
+	LL_UNITDATA_IND,	/* TLLI, SN-PDU */
+	LL_STATUS_IND,		/* TLLI, Cause */
+};
+
+/* Section 4.5.2 Logical Link States + Annex C.2 */
+enum gprs_llc_lle_state {
+	GPRS_LLES_UNASSIGNED	= 1,	/* No TLLI yet */
+	GPRS_LLES_ASSIGNED_ADM	= 2,	/* TLLI assigned */
+	GPRS_LLES_LOCAL_EST	= 3,	/* Local Establishment */
+	GPRS_LLES_REMOTE_EST	= 4,	/* Remote Establishment */
+	GPRS_LLES_ABM		= 5,
+	GPRS_LLES_LOCAL_REL	= 6,	/* Local Release */
+	GPRS_LLES_TIMER_REC 	= 7,	/* Timer Recovery */
+};
+
+enum gprs_llc_llme_state {
+	GPRS_LLMS_UNASSIGNED	= 1,	/* No TLLI yet */
+	GPRS_LLMS_ASSIGNED	= 2,	/* TLLI assigned */
+};
+
+/* Section 8.9.9 LLC layer parameter default values */
+struct gprs_llc_params {
+	uint16_t iov_i_exp;
+	uint16_t t200_201;
+	uint16_t n200;
+	uint16_t n201_u;
+	uint16_t n201_i;
+	uint16_t mD;
+	uint16_t mU;
+	uint16_t kD;
+	uint16_t kU;
+};
+
+/* Section 4.7.1: Logical Link Entity: One per DLCI (TLLI + SAPI) */
+struct gprs_llc_lle {
+	struct llist_head list;
+
+	uint32_t sapi;
+
+	struct gprs_llc_llme *llme;
+
+	enum gprs_llc_lle_state state;
+
+	struct osmo_timer_list t200;
+	struct osmo_timer_list t201;	/* wait for acknowledgement */
+
+	uint16_t v_sent;
+	uint16_t v_ack;
+	uint16_t v_recv;
+
+	uint16_t vu_send;
+	uint16_t vu_recv;
+
+	/* non-standard LLC state */
+	uint16_t vu_recv_last;
+	uint16_t vu_recv_duplicates;
+
+	/* Overflow Counter for ABM */
+	uint32_t oc_i_send;
+	uint32_t oc_i_recv;
+
+	/* Overflow Counter for unconfirmed transfer */
+	uint32_t oc_ui_send;
+	uint32_t oc_ui_recv;
+
+	unsigned int retrans_ctr;
+
+	struct gprs_llc_params params;
+};
+
+#define NUM_SAPIS	16
+
+struct gprs_llc_llme {
+	struct llist_head list;
+
+	enum gprs_llc_llme_state state;
+
+	uint32_t tlli;
+	uint32_t old_tlli;
+
+	/* Crypto parameters */
+	enum gprs_ciph_algo algo;
+	uint8_t kc[16];
+	uint8_t cksn;
+	/* 3GPP TS 44.064 § 8.9.2: */
+	uint32_t iov_ui;
+
+	/* over which BSSGP BTS ctx do we need to transmit */
+	uint16_t bvci;
+	uint16_t nsei;
+	struct gprs_llc_lle lle[NUM_SAPIS];
+
+	/* Copy of the XID fields we have sent with the last
+	 * network originated XID-Request. Since the phone
+	 * may strip the optional fields in the confirmation
+	 * we need to remeber those fields in order to be
+	 * able to create the compression entity. */
+	struct llist_head *xid;
+
+	/* Compression entities */
+	struct {
+		/* In these two list_heads we will store the
+		 * data and protocol compression entities,
+		 * together with their compression states */
+		struct llist_head *proto;
+		struct llist_head *data;
+	} comp;
+
+	/* Internal management */
+	uint32_t age_timestamp;
+};
+
+#define GPRS_LLME_RESET_AGE (0)
+
+extern struct llist_head gprs_llc_llmes;
+
+/* LLC low level types */
+
+enum gprs_llc_cmd {
+	GPRS_LLC_NULL,
+	GPRS_LLC_RR,
+	GPRS_LLC_ACK,
+	GPRS_LLC_RNR,
+	GPRS_LLC_SACK,
+	GPRS_LLC_DM,
+	GPRS_LLC_DISC,
+	GPRS_LLC_UA,
+	GPRS_LLC_SABM,
+	GPRS_LLC_FRMR,
+	GPRS_LLC_XID,
+	GPRS_LLC_UI,
+};
+
+struct gprs_llc_hdr_parsed {
+	uint8_t sapi;
+	uint8_t is_cmd:1,
+		 ack_req:1,
+		 is_encrypted:1;
+	uint32_t seq_rx;
+	uint32_t seq_tx;
+	uint32_t fcs;
+	uint32_t fcs_calc;
+	uint8_t *data;
+	uint16_t data_len;
+	uint16_t crc_length;
+	enum gprs_llc_cmd cmd;
+};
+
+
+/* BSSGP-UL-UNITDATA.ind */
+int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv);
+
+/* LL-UNITDATA.req */
+int gprs_llc_tx_ui(struct msgb *msg, uint8_t sapi, int command,
+		   struct sgsn_mm_ctx *mmctx, bool encryptable);
+
+/* Chapter 7.2.1.2 LLGMM-RESET.req */
+int gprs_llgmm_reset(struct gprs_llc_llme *llme);
+int gprs_llgmm_reset_oldmsg(struct msgb* oldmsg, uint8_t sapi,
+			    struct gprs_llc_llme *llme);
+
+/* Set of LL-XID negotiation (See also: TS 101 351, Section 7.2.2.4) */
+int gprs_ll_xid_req(struct gprs_llc_lle *lle,
+		    struct gprs_llc_xid_field *l3_xid_field);
+
+/* 04.64 Chapter 7.2.1.1 LLGMM-ASSIGN */
+int gprs_llgmm_assign(struct gprs_llc_llme *llme,
+		      uint32_t old_tlli, uint32_t new_tlli);
+int gprs_llgmm_unassign(struct gprs_llc_llme *llme);
+
+int gprs_llc_init(const char *cipher_plugin_path);
+int gprs_llc_vty_init(void);
+
+/**
+ * \short Check if N(U) should be considered a retransmit
+ *
+ * Implements the range check as of GSM 04.64 8.4.2
+ * Receipt of unacknowledged information.
+ *
+ * @returns Returns 1 if  (V(UR)-32) <= N(U) < V(UR)
+ * @param nu N(U) unconfirmed sequence number of the UI frame
+ * @param vur V(UR) unconfirmend received state variable
+ */
+static inline int gprs_llc_is_retransmit(uint16_t nu, uint16_t vur)
+{
+	int delta = (vur - nu) & 0x1ff;
+	return 0 < delta && delta < 32;
+}
+
+/* LLC low level functions */
+void gprs_llme_copy_key(struct sgsn_mm_ctx *mm, struct gprs_llc_llme *llme);
+
+/* parse a GPRS LLC header, also check for invalid frames */
+int gprs_llc_hdr_parse(struct gprs_llc_hdr_parsed *ghp,
+		       uint8_t *llc_hdr, int len);
+void gprs_llc_hdr_dump(struct gprs_llc_hdr_parsed *gph, struct gprs_llc_lle *lle);
+int gprs_llc_fcs(uint8_t *data, unsigned int len);
+
+
+/* LLME handling routines */
+struct llist_head *gprs_llme_list(void);
+struct gprs_llc_lle *gprs_lle_get_or_create(const uint32_t tlli, uint8_t sapi);
+
+
+#endif